The purpose of this research is to understand the relation between the parameters of impulse noise (peak pressure, duration, number, repetition rate, exposure duration, etc.) and the effects on hearing as assessed by anatomical, physiological and psychophysical techniques in the chinchilla. Several mechanical or electrical-mechanical devices are used to produce realistic noise impacts. Exposure paradigms are designed to produce asymptotic threshold shifts over exposure durations lasting up to 40 days. Variations of the exposure paradigm include "work week" schedules. Studies are designed to maximize data acquisition to answer basic questions concerning the development of impulse noise damage risk criteria, e.g., validity of the equal energy hypothesis; the effects of noise level during recovery periods, etc. Routine data collection consists of surface preparation derived cochleograms and evoked response and behavioral audiograms and tuning curves. More detailed studies of certain experimental groups will include scanning E.M., as well as more discriminating psychoacoustic measures of hearing. Correlations among the various realms of data are essential for the development of a scientifically based damage risk criteria.